It is fully recognized through disclosures in patent publications and a large number of general references that vitamin D.sub.3 metabolites play an extremely important role as substances controlling the metabolism of calcium and phosphates in the body. Recently, further, an increase has been seen in clinical application as drugs for the treatment of various diseases such as with the numerous vitamin D.sub.3 metabolites found to have the function of inducing differentiation of tumorous bone marrow cells. On the other hand, recently, a novel vitamin D.sub.3 active metabolite having an .alpha.-hydroxylactone ring at the steroid side chain has been found. [Arch. Bio-chem. Biophys., 204, 339-391 (1980); FEBS LETTERS, 134, 207-211 (1981)]. This compound is 1.alpha.,25-dihydroxy-vitamin D.sub.3 -26,23-lactone and is represented by the following structural formula: ##STR3##
This compound has been reported to have an action for reducing the concentration of calcium in blood serum (Japanese Unexamined Patent Publication (Kokai) No. 58-118516), an action for suppressing the proliferation of tumor cells (Japanese Unexamined Patent Publication (Kokai) No. 58-210011), an action for promoting bone formation (Japanese Unexamined Patent Publication (Kokai) No. 60-185715), etc.